The present invention relates to a method for producing a thin film semiconductor device, and to a device produced by said method. In particular, it relates to such a method and a device in which an amorphous silicon layer is deposited on a substrate which is subject to crystallization through an annealing process at lower temperature and high growth rate.
Conventionally, a poly silicon layer, which is used for a thin film transistor, is produced through the steps of producing an amorphous silicon layer, and crystallizing said layer through a laser annealing process or a thermal solid phase growth process. The characteristics of the crystallized poly silicon thus produced depend upon a method used for producing said amorphous silicon.
Conventionally, an amorphous silicon layer is produced through a low pressure CVD process (LPCVD) or a plasma CVD process (P-CVD) using as the raw material SiH4, or Si2H6. The characteristics of a thin film transistor made using said amorphous silicon layer, or the mobility in the layer, are better when the amorphous silicon layer is produced at lower temperature, and at higher growth rate, or speed, of the layer.
In comparing P-CVD with LPCVD, P-CVD process has the disadvantage as compared with LPCVD process in that the former introduces impurity like oxygen into the amorphous layer due to activation of the gas, including oxygen, in a reaction chamber, although the former produces an amorphous layer at lower temperature than the latter, and therefore, it is impossible for P-CVD process to provide better characteristics than LPCVD process (IEEE ELECTRON DEVICE LETTERS, VOL. 12, No. 7, July 1991). Further, since, the process shown in that article uses high pressure oxygen to provide an oxidized layer on an amorphous layer for a gate insulation layer, it would be possible that the amorphous layer includes more undesired oxygen.
As another prior art, the laid open JP patent 66919/1988 shows a process for producing an amorphous layer by using a gas comprising Si2Cl6+SiH4, or Si2Cl6+Si2H6. However, the process is not a mere thermal dissolution process, but an optical dissolution process and/or a plasma discharge process, and therefore, the apparatus used to carry out this process is complicated, and producing cost would be high. The quality of the layer produced through said process is not shown in that publication.
Said optical dissolution process has the disadvantage that the amorphous silicon layer is produced only in an area where light illuminates on a substrate.
Said plasma dissolution process also has the disadvantage that producing efficiency is low since only one substrate is placed in vertical direction on a board holder in a heater. Further, since the operating chamber must be conductive for applying voltage for producing the plasma, and it is actually made of stainless steel, metal pollution of the gas, and therefore the amorphous layer, is inevitable. Further, since the gas material has undesired etching ability, it is difficult to produce an amorphous silicon layer through said process.
It is an object, therefore, of the present invention to overcome the disadvantages and limitations of a process for producing a prior thin film semiconductor device by providing a new and improved process for producing a thin film semiconductor device.
It is also an object of the present invention to provide a method for producing a thin film semiconductor device by using a non-conductive chamber.
It is also an object of the present invention to provide a method for producing a thin film semiconductor device by using a quartz crystal chamber.
Another object of the present invention is to provide a method for producing a thin film semiconductor device with high producing efficiency, and excellent characteristics.
Another object of the present invention is to provide a semiconductor device produced by said method, and having excellent characteristics in particular high mobility and low threshold voltage.
The above and other objects are attained by a method for producing a thin film semiconductor device comprising the steps of producing an amorphous silicon layer on a substrate through a CVD process with gas comprising a silane SinH2(n+1), where n is an integer, having chlorine Cl2 added thereto, and effecting solid phase growth of said amorphous silicon layer thereby providing active silicon layer.
A semiconductor device thus produced has an active silicon layer which includes chlorine in a concentration in the range of about 2xc3x971017/cm3 to 5xc3x971021 atom/cm3, and has high mobility and low threshold voltage.